Key Points
- Investigate the mechanical and biochemical transitions of the muscle cross-bridge cycle and determine how calcium ions regulate cross-bridge attachment states.
- Applied laser photolysis to release caged ATP[gamma S] within permeabilized muscle fibers locked in rigor across varied calcium concentrations (<1 nM to 30 µM).
- Recorded active tension, fiber stiffness, and tension recovery following ramp stretches of varying velocities.
- Photolysis of caged ATP[gamma S] fully relaxed tension without the transient force increase seen with regular ATP, indicating ATP hydrolysis normally precedes mechanical force generation.
- In the presence of Ca2+, fibers relaxed fully while maintaining significant stiffness, which also formed when Ca2+ was elevated from <1 nM to 30 µM in the presence of ATP[gamma S].
- Tension responses to ramp stretches increased with stretch velocity in the presence of Ca2+ and ATP[gamma S], revealing cross-bridge detachment rate constants extending into the 10^3 s^-1 range.
Structured PICO
PPopulationPermeabilized muscle fibers in rigor
IInterventionAdenosine 5'-[gamma-thio]triphosphate (ATP[gamma S]) and laser photolysis of caged ATP[gamma S]
CComparatorATP and caged ATP
OOutcomeMuscle tension and stiffnesssurrogate
This basic science study demonstrates that the calcium-regulatory system can directly control the attachment of muscle cross-bridges prior to the power stroke.